part 4] ]sroRiTE or sierea leoxe. 837 



particularly refer are the alteration of basic lavas hj the Shap 

 Granite, 1 and of the Ej'-cott lavas by the Carrock-Fell Gabbro " and 

 the Eskdale Granite.^ The changes induced in these cases *^' consist 

 ■essentially of the conversion of pyroxenes to amphiboles, the 

 ■recrystallization of the felspars into a mosaic, and the development 

 of brown biotite ; locally, garnets, sphene, and other minerals are 

 developed. The Grainsgill Granophyi-e ^ altered the augite of 

 iihe Carrock-Fell Gabbro locally into compact brown hornblende, 

 formed granular sphene from the ilmenite and felspar, and con- 

 verted the felspar into secondarj'' minerals. Exam])'es are given 

 in the Skye Survey Memoir of gabbro enclosing xenoliths (1) of 

 ultrabasic rocks and (2) of an earlier gabbro ; in the first case it 

 is stated that no clear indication of thermal metamorphism occurs, 

 a-nd in the second no mention of any alteration is made.^ 



Prof, Lacroix, in the course of his studies on the inclusions of 

 volcanic rocks, was able to consider in detail the effect of basic 

 magmas on coarse-grained basic and ultrabasic xenoliths ; but, so 

 far as possible, he satisfied himself beforehand that the xenoliths 

 were still fresli at the time when they were first attacked by the 

 magma. In a later paragraph his results will be compared with 

 those obtained in Sierra Leone. Although in the course of building 

 up the complex described above, the invading magmas themselves 

 ■did not suffer any appreciable modification, the rocks invaded were 

 nevei'theless subjected to a more or less intense contact-metamor- 

 phism. The more important examples of this metamorphism occur 

 in the older or normal norite where it has been invaded by : — 



(1) A. The younger norite. 

 B. The beerbachite. 



(2) A. The norite-aplite. 

 B. The clolerite. 



The alteration of the older norite effected by (1) the younger 

 norite and the beerbachite, differed from that due to (2) the 

 aplite-veins and the dolerite, in the following important par- 

 ticulars : — 



(a) Magnitude . — The intrusions of the first group were much larger than 

 those of the second group, and accordingly they were able to incorporate 

 innumerable large and small fragments of the older norite. An examination 

 of these fragments has afforded excellent material for a study of the corrosion 



i A. Harker & J. E. Marr, Q. J. G. S. vol. xlix (1893). 



^ A. Harker, ' Carrock Fell ; a Study in the Variation of Igneous Rock- 

 Masses : Part I— the Gabbro ' Ihid. vol. 1 (1894) p. 334. 



•^ E. E. Walker. ' Notes on the Garnet-bearing & Associated Rocks of 

 the Borrowdale Volcanic Series ' Ihid. vol. Ix (1904) p. 102. 



"^ See also the metamorphism of basalt by Cuillin gabbro, ' The Geology of 

 Glenelg, Lochalsh, & the South- East Part of Skye ' Mem. Geol. Surv. Scot. 

 1910, p. 145 ; and ' The Tertiary Igneous Rocks of Skye ' Mem. Geol. Surv. 

 1904, p. 122. 



^ A. Harker, Q. J. G. S. vol. 1 (1894) p. 334. 



*'' 'The Tertiary Igneous Rocks of Skye' Mem. Geol. ^'iirv. 1904, pp. 99 

 A 121. 



